1. Field of the Invention
The present invention relates to an on-vehicle battery condition estimation device capable of estimating the condition of a battery mounted to a vehicle for starting an internal combustion engine and to supply electric power to various types of electrical control devices.
2. Description of the Related Art
An on-vehicle battery serves as a device to supply an engine starter in order to start the operation of an internal combustion engine and serves as an electric power supplying device to supply electric power to various types of electrical control devices. In order to ensure the steady supply of an electric power to those electrical control devices, that is, to keep the reliability in operation of those electrical control devices, and to prevent remarkable deterioration in quality of the on-vehicle battery caused by over-discharge, the on-vehicle battery must be kept at a voltage of not less than its lower limit voltage.
When the vehicle is equipped with an idling stop control system, it is required to estimate the lower limit voltage of the on-vehicle battery in order to keep the voltage of the on-vehicle battery, which is decreased by the engine start operation, not less than its lower limit voltage, and in order also to keep the battery voltage capable of supplying a necessary amount of electric power to an engine starter.
There are various conventional devices for estimating the lower limit voltage of an on-vehicle battery mounted to a vehicle. For example, Japanese patent laid open publication No. JP 2006-258070 disclosed a conventional technique to estimate a charging condition of the on-vehicle battery when the vehicle stops and to allow the execution of the idling stop control to automatically stop the internal combustion engine of the vehicle when the on-vehicle battery has a charged electric power to start the internal combustion engine.
In addition, JP 2007-223530 has disclosed another conventional technique to estimate an internal resistance value of the on-vehicle battery for use to estimate a voltage drop of an on-vehicle battery when an internal combustion engine restarts.
However, the above conventional techniques calculate a necessary electric power based on an internal resistance value of the on-vehicle battery that is estimated when the internal combustion engine starts, and then permit the execution of the idling stop control when the on-vehicle battery stores the electric power of not less than a necessary electric power to start the internal combustion engine. The conventional control operations described above do not detect how long the idling stop control can be performed. That is, even if the vehicle is under the idling stop control, it is necessary to perform the electric power generation by the internal combustion engine when the voltage of the on-vehicle battery drops. In this case, the idling stop control must be halted. When the above idling stop control is performed under using the inadequately estimation results described above, the on-vehicle battery is deteriorated and may inconvenience the driver and passengers.